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Applicability of similarity principles to structural models

Description: From Summary: "A systematic account is given in part I of the use of dimensional analysis in constructing similarity conditions for models and structures. The analysis covers large deflections, buckling, plastic behavior, and materials with nonlinear stress-strain characteristics, as well as the simpler structural problems."
Date: July 1944
Creator: Goodier, J N & Thomson, W T
Partner: UNT Libraries Government Documents Department

Theoretical Study of Si and N Adsorption on the Si-terminated SiC (001) Surface

Description: We report the results of first principles molecular dynamics simulations of the adsorption of Si and N atoms on a Si-terminated p(2 x 1) SiC(001) surface. In particular, we discuss different structural models for the Si-rich (3 x 2) surface, and the adsorption of 1/8, 1/2 and 1 monolayer nitrogen on the p(2 x 1) surface. Our simulations show that a SiC(001)-p(2 x 1) surface covered by a nitrogen monolayer is an inert substrate which inhibits growth.
Date: October 26, 1999
Creator: Pizzagalli, L.; Catellani, A.; Galli, G.; Gygi, F. & Baratoff, A.
Partner: UNT Libraries Government Documents Department


Description: M&D Professional Services, Inc. (M&D) is under subcontract to Pacific Northwest National Laboratories (PNNL) to perform seismic analysis of the Hanford Site Double-Shell Tanks (DSTs) in support of a project entitled ''Double-Shell Tank DSV Integrity Project-DST Thermal and Seismic Analyses''. The overall scope of the project is to complete an up-to-date comprehensive analysis of record of the DST System at Hanford in support of Tri-Party Agreement Milestone M-48-14. The thermal and operating loads analysis of the DSTs is documented in Rinker et al. (2004). The work statement provided to M&D (PNNL 2003) required that the seismic analysis of the DST assess the impacts of potentially non-conservative assumptions in previous analyses and account for the additional soil mass due to the as-found soil density increase, the effects of material degradation, additional thermal profiles applied to the full structure including the soil-structure response with the footings, the non-rigid (low frequency) response of the tank roof, the asymmetric seismic-induced soil loading, the structural discontinuity between the concrete tank wall and the support footing and the sloshing of the tank waste. The seismic analysis considers the interaction of the tank with the surrounding soil, and the effects of the primary tank contents. The DST and the surrounding soil are modeled as a system of finite elements. The depth and width of the soil incorporated into the analysis model are sufficient to obtain appropriately accurate analytical results. The analyses required to support the work statement differ from previous analysis of the DSTs in that the soil-structure interaction (SSI) model includes several (nonlinear) contact surfaces in the tank structure, and the contained waste must be modeled explicitly in order to capture the fluid-structure interaction behavior between the primary tank and contained waste. Soil-structure interaction analyses are traditionally solved in the frequency domain, but frequency domain analysis ...
Date: March 14, 2006
Creator: MACKEY, T.C.
Partner: UNT Libraries Government Documents Department

Discussion of model calibration and validation for transient dynamics simulation.

Description: Model calibration refers to a family of inverse problem-solving numerical techniques used to infer the value of parameters from test data sets. The purpose of model calibration is to optimize parametric or non-parametric models in such a way that their predictions match reality. In structural dynamics an example of calibration is the finite element model updating technology. Our purpose is essentially to discuss calibration in the broader context of model validation. Formal definitions are proposed and the notions of calibration and validation are illustrated using an example of transient structural dynamics that deals with the propagation of a shock wave through a hyper-foam pad. An important distinction that has not been made in finite element model updating and that is introduced here is that parameters of the numerical models or physical tests are categorized into input parameters, calibration variables, controllable and uncontrollable variables. Such classification helps to define model validation goals. Finally a path forward for validating numerical model is discussed and the relationship with uncertainty assessment is stressed.
Date: January 1, 2001
Creator: Hemez, Fran├žois M.; Doebling, Scott W. & Wilson, Amanda C.
Partner: UNT Libraries Government Documents Department

A Markov-Chain Monte-Carlo Based Method for Flaw Detection in Beams

Description: A Bayesian inference methodology using a Markov Chain Monte Carlo (MCMC) sampling procedure is presented for estimating the parameters of computational structural models. This methodology combines prior information, measured data, and forward models to produce a posterior distribution for the system parameters of structural models that is most consistent with all available data. The MCMC procedure is based upon a Metropolis-Hastings algorithm that is shown to function effectively with noisy data, incomplete data sets, and mismatched computational nodes/measurement points. A series of numerical test cases based upon a cantilever beam is presented. The results demonstrate that the algorithm is able to estimate model parameters utilizing experimental data for the nodal displacements resulting from specified forces.
Date: September 28, 2006
Creator: Glaser, R E; Lee, C L; Nitao, J J; Hickling, T L & Hanley, W G
Partner: UNT Libraries Government Documents Department

Structural Models of Amorphous Carbon and its Surfaces by Tight-Binding Molecular Dynamics

Description: We use liner-scaling tight-binding molecular dynamics to generate three structural models of bulk amorphous carbon with different atomic density. Amorphous carbon surfaces are then obtained by imposing tensile strain on these computer generated networks until fracture occurs. Our results show that for a given density, the formation energy of surfaces obtained with different tensile strains differ by only a few 10{sup -1} eV/atom and their structural properties are qualitatively similar. The presence of sp sites at the surface is observed at all densities, but with different values of the concentration. The surface thicknesses obtained in our simulations agree with experimental data. Furthermore we find that surface roughness increases with the amount of graphitic component in the bulk sample. The same trends of the macroscopic properties are obtained when using a two-center tight-binding Hamiltonian, an environmental dependent one, and first principles calculations.
Date: October 26, 1999
Creator: Haerle, R.; Baldereschi, A. & Galli, G.
Partner: UNT Libraries Government Documents Department

Flash vacuum pyrolysis of lignin model compounds

Description: Despite the extensive research into the pyrolysis of lignin, the underlying chemical reactions that lead to product formation are poorly understood. Detailed mechanistic studies on the pyrolysis of biomass and lignin under conditions relevant to current process conditions could provide insight into utilizing this renewable resource for the production of chemicals and fuel. Currently, flash or fast pyrolysis is the most promising process to maximize the yields of liquid products (up to 80 wt %) from biomass by rapidly heating the substrate to moderate temperatures, typically 500{degrees}C, for short residence times, typically less than two seconds. To provide mechanistic insight into the primary reaction pathways under process relevant conditions, we are investigating the flash vacuum pyrolysis (FVP) of lignin model compounds that contain a {beta}-ether. linkage and {alpha}- or {gamma}-alcohol, which are key structural elements in lignin. The dominant products from the FVP of PhCH{sub 2}CH{sub 2}OPh (PPE), PhC(OH)HCH{sub 2}OPh, and PhCH{sub 2}CH(CH{sub 2}OH)OPh at 500{degrees}C can be attributed to homolysis of the weakest bond in the molecule (C-O bond) or 1,2-elimination. Surprisingly, the hydroxy-substituent dramatically increases the decomposition of PPE. It is proposed that internal hydrogen bonding is accelerating the reaction.
Date: March 1, 1997
Creator: Cooney, M.J.; Britt, P.F. & Buchanan, A.C. III
Partner: UNT Libraries Government Documents Department

APT/LEDA RFQ and support frame structural analysis

Description: This report documents structural analysis of the Accelerator Production of Tritium Low Energy Demonstration Accelerator (APT/LEDA) Radio Frequency Quadrupole (RFQ) accelerator structure and its associated support frame. This work was conducted for the Department of Energy in support of the APT/LEDA. Structural analysis of the RFQ was performed to quantify stress levels and deflections due to both vacuum loading and gravity loading. This analysis also verified the proposed support scheme geometry and quantified interface loads. This analysis also determined the necessary stiffness and strength requirements of the RFQ support frame verifying the conceptual design geometry and allowing specification of individual frame elements. Complete structural analysis of the frame was completed subsequently. This report details structural analysis of the RFQ assembly with regard to gravity and vacuum loads only. Thermally induced stresses from the Radio Frequency (RF) surface resistance heating were not considered.
Date: April 1, 1997
Creator: Ellis, S.
Partner: UNT Libraries Government Documents Department

Structural system identification: Structural dynamics model validation

Description: Structural system identification is concerned with the development of systematic procedures and tools for developing predictive analytical models based on a physical structure`s dynamic response characteristics. It is a multidisciplinary process that involves the ability (1) to define high fidelity physics-based analysis models, (2) to acquire accurate test-derived information for physical specimens using diagnostic experiments, (3) to validate the numerical simulation model by reconciling differences that inevitably exist between the analysis model and the experimental data, and (4) to quantify uncertainties in the final system models and subsequent numerical simulations. The goal of this project was to develop structural system identification techniques and software suitable for both research and production applications in code and model validation.
Date: April 1, 1997
Creator: Red-Horse, J.R.
Partner: UNT Libraries Government Documents Department

Active chatter control in a milling machine

Description: The use of active feedback compensation to mitigate cutting instabilities in an advanced milling machine is discussed in this paper. A linear structural model delineating dynamics significant to the onset of cutting instabilities was combined with a nonlinear cutting model to form a dynamic depiction of an existing milling machine. The model was validated with experimental data. Modifications made to an existing machine model were used to predict alterations in dynamics due to the integration of active feedback compensation. From simulations, subcomponent requirements were evaluated and cutting enhancements were predicted. Active compensation was shown to enable more than double the metal removal rate over conventional milling machines. 25 refs., 10 figs., 1 tab.
Date: August 1, 1997
Creator: Dohner, J.L.; Hinnerichs, T.D. & Lauffer, J.P.
Partner: UNT Libraries Government Documents Department

Structural model uncertainty in stochastic simulation

Description: Prediction uncertainty in stochastic simulation models can be described by a hierarchy of components: stochastic variability at the lowest level, input and parameter uncertainty at a higher level, and structural model uncertainty at the top. It is argued that a usual paradigm for analysis of input uncertainty is not suitable for application to structural model uncertainty. An approach more likely to produce an acceptable methodology for analyzing structural model uncertainty is one that uses characteristics specific to the particular family of models.
Date: September 1, 1997
Creator: McKay, M.D. & Morrison, J.D.
Partner: UNT Libraries Government Documents Department


Description: We report results of foam-rubber modeling of the effect of a shallow weak layer on ground motion from strike-slip ruptures. Computer modeling of strong ground motion from strike-slip earthquakes has involved somewhat arbitrary assumptions about the nature of slip along the shallow part of the fault (e.g., fixing the slip to be zero along the upper 2 kilometers of the fault plane) in order to match certain strong motion accelerograms. Most modeling studies of earthquake strong ground motion have used what is termed kinematic dislocation modeling. In kinematic modeling the time function for slip on the fault is prescribed, and the response of the layered medium is calculated. Unfortunately, there is no guarantee that the model and the prescribed slip are physically reasonable unless the true nature of the medium and its motions are known ahead of time. There is good reason to believe that in many cases faults are weak along the upper few kilometers of the fault zone and may not be able to maintain high levels of shear strain required for high dynamic energy release during earthquakes. Physical models of faulting, as distinct from numerical or mathematical models, are guaranteed to obey static and dynamic mechanical laws. Foam-rubber modeling studies have been reported in a number of publications. The object of this paper is to present results of physical modeling using a shallow weak layer, in order to verify the physical basis for assuming a long rise time and a reduced high frequency pulse for the slip on the shallow part of faults. It appears a 2-kilometer deep, weak zone along strike-slip faults could indeed reduce the high frequency energy radiated from shallow slip, and that this effect can best be represented by superimposing a small amplitude, short rise-time pulse at the onset of a much longer ...
Date: February 23, 1998
Creator: Brune, James N. & Anooshehpoor, Abdolrasool
Partner: UNT Libraries Government Documents Department

Evaluating uncertainty in simulation models

Description: The authors discussed some directions for research and development of methods for assessing simulation variability, input uncertainty, and structural model uncertainty. Variance-based measures of importance for input and simulation variables arise naturally when using the quadratic loss function of the difference between the full model prediction y and the restricted prediction {tilde y}. The concluded that generic methods for assessing structural model uncertainty do not now exist. However, methods to analyze structural uncertainty for particular classes of models, like discrete event simulation models, may be attainable.
Date: December 1, 1998
Creator: McKay, M.D.; Beckman, R.J.; Morrison, J.D. & Upton, S.C.
Partner: UNT Libraries Government Documents Department

A Validation of Bayesian Finite Element Model Updating for Linear Dynamics

Description: This work addresses the issue of statistical model updating and correlation. The updating procedure is formulated to improve the predictive quality of a structural model by minimizing out-of-balance modal forces. It is shown how measurement and modeling uncertainties can be taken into account to provide not only the correlated model but also the associated confidence levels. Hence, a Bayesian parameter estimation technique is derived and its numerical implementation is discussed. Two demonstration examples that involve test-analysis correlation with real test data are presented. First, the validation of an engine cradle model used in the automotive industry shows how the design's uncertainties can be reduced via model updating. The second example consists of employing test-analysis correlation for identifying the degree of nonlinearity of the LANL 8-DOF testbed.
Date: February 8, 1999
Creator: Hemez, F.M. & Doebling, S.W.
Partner: UNT Libraries Government Documents Department

Corrector magnets: Combined structural analysis of collider 50 mm aperture ordered wound quadrupoles interior section

Description: The 50mm aperture prototype collider ordered wound quadrupole corrector magnets have been modeled with finite element techniques considering the individual and combined load cases of the preloading from keys, cooldown to 4 K and the effect of magnetic forces during energizing. Results of the analysis are presented as longitudinal, transverse and shear stresses for the ordered wound coils and as maximum von Mises stress for the carbon steel outer laminations, the stainless steel inner lamination, and the carbon steel keys.
Date: April 1, 1993
Creator: Tran, Vu H.
Partner: UNT Libraries Government Documents Department


Description: This document is the annual technical progress report for Department of Energy Contract No. DE-FC26-00NT41026 entitled Proof-of-Concept Research for an Advanced Design Criterion to Improve Working Gas Capacity for Natural Gas Storage Caverns in Salt Formations. This report covers the reporting period from October 1, 2000, through September 30, 2001. During this reporting period, the project was initiated and work was performed to develop structural models that will be used to evaluate two compressed natural gas storage caverns in the McIntosh Dome northwest of Mobile, Alabama. Information necessary to define the structural models include site-specific stress, temperature, geometry, stratigraphy, and operating scenarios in the dome and for the caverns. Additionally, material model development for the salt at the McIntosh Dome was initiated. Material model development activities include acquisition of salt core for testing, laboratory testing, and regression analyses to determine site-specific model parameter values that describe the behavior of salt around a storage cavern. Although not performed during this reporting period, the information and models developed will be used to perform advanced design storage cavern analyses for the Bay Gas caverns to determine the operating pressure ranges to maintain stable conditions.
Date: December 1, 2001
Creator: DeVries, Kerry L.; Mellegard, Kirby D. & Callahan, Gary D.
Partner: UNT Libraries Government Documents Department

A demonstration of simple airfoils: Structural design and materials choices

Description: An educational unit is presented for building and evaluating simple wing structures, in order to learn about materials choice and lightweight construction. This unit is appropriate for a high school materials science class or lower-division college courses in structural engineering, materials science, or aeronautical engineering.
Date: January 1, 1993
Creator: Bunnell, L.R. (Pacific Northwest Lab., Richland, WA (United States)) & Piippo, S.W. (Richland School District, WA (United States))
Partner: UNT Libraries Government Documents Department

A demonstration of simple airfoils: Structural design and materials choices

Description: An educational unit is presented for building and evaluating simple wing structures, in order to learn about materials choice and lightweight construction. This unit is appropriate for a high school materials science class or lower-division college courses in structural engineering, materials science, or aeronautical engineering.
Date: January 1, 1993
Creator: Bunnell, L. R. & Piippo, S. W.
Partner: UNT Libraries Government Documents Department

Reflectional transformation for structural stiffness

Description: This paper presents a structural reflection-related transformation for structural stiffness. The stiffness transformation addresses reflection of a structure about any of the three coordinate planes and renders the desired stiffness matrix using a stiffness matrix for the same structure before reflection. This transformation is elegant and simple, provides an efficient and technically rigorous approach to derive the required stiffness matrix without structural remodeling, and can be readily programmed to quickly perform the required matrix manipulations. 2 figs.
Date: January 1, 1990
Creator: Vashi, K.M.
Partner: UNT Libraries Government Documents Department

Synthesis of a naphthalene-hydroxynaphthalene polymer model compound. Quarterly report, December 13, 1990--March 12, 1991

Description: The objective of this contract is the synthesis of a new naphthalene-hydroxynaphthalene polymer model compound for coal combustion studies. This effort also requires the development of a synthetic procedure for this compound since it has not been reported before. We can only report that we are still unable to provide the target polymer or even any of the key intermediates leading to this target Dr. Rao has been informed of our progress (or lack of progress), and he has suggested that we begin to design other alternative compounds which contain the functionalities required by the target compound. In response to this suggestion, we have quickly designed the potential targets shown in Scheme VIL We are currently evaluating the schemes further and we will continue designing routes to the other analogous compounds.
Date: April 15, 1991
Creator: Kwong, C. D.
Partner: UNT Libraries Government Documents Department

Volcanic studies at Katmai

Description: The Continental Scientific Drilling Program (CSDP) is a national effort supported by the Department of Energy, the US Geological Survey, and the National Science Foundation. One of the projects proposed for the CSDP consists of drilling a series of holes in Katmai National Park in Alaska to give a third dimension to the model of the 1912 eruption of Novarupta, and to investigate the processes of explosive volcanism and hydrothermal transport of metals (Eichelberger et al., 1988). The proposal for research drilling at Katmai states that ``the size, youth, elevated temperature, and simplicity of the Novarupta vent make it a truly unique scientific target.`` The National Park Service (NPS), which has jurisdiction, is sympathetic to aims of the study. However, NPS wishes to know whether Katmai is indeed uniquely suited to the research, and has asked the Interagency Coordinating Group to support an independent assessment of this claim. NPS suggested the National Academy of Sciences as an appropriate organization to conduct the assessment. In response, the National Research Council -- the working arm of the Academy -- established, under the aegis of its US Geodynamics Committee, a panel whose specific charge states: ``The proposed investigation at Katmai has been extensively reviewed for scientific merit by the three sponsoring and participating agencies. Thus, the scientific merit of the proposed drilling at Katmai is not at issue. The panel will review the proposal for scientific drilling at Katmai and prepare a short report addressing the specific question of the degree to which it is essential that the drilling be conducted at Katmai as opposed to volcanic areas elsewhere in the world.``
Date: December 31, 1989
Partner: UNT Libraries Government Documents Department

Visible Light-Induced Electron Transfer from Di-mu-oxo Bridged Dinuclear Mn Complexes to Cr Centers in Silica Nanopores

Description: The compound (bpy)2MnIII(mu-O)2MnIV(bpy)2, a structural model relevant for the photosynthetic water oxidation complex, was coupled to single CrVI charge-transfer chromophores in the channels of the nanoporous oxide AlMCM-41. Mn K-edge EXAFS spectroscopy confirmed that the di-mu-oxo dinuclear Mn core of the complex is unaffected when loaded into the nanoscale pores. Observation of the 16-line EPR signal characteristic of MnIII(mu-O)2MnIV demonstrates that the majority of the loaded complexes retained their nascent oxidation state in the presence or absence of CrVI centers. The FT-Raman spectrum upon visible light excitation of the CrVI-OII --> CrV-OI ligand-to-metal charge-transfer reveals electron transfer from MnIII(mu-O)2MnIV (Mn-O stretch at 700 cm-1) to CrVI, resulting in the formation of CrV and MnIV(mu-O)2MnIV (Mn-O stretch at 645 cm-1). All initial and final states are directly observed by FT-Raman or EPR spectroscopy, and the assignments corroborated by X-ray absorption spectroscopy measurements. The endoergic charge separation products (DELTA Eo = -0.6 V) remain after several minutes, which points to spatial separation of CrV and MnIV(mu-O)2MnIV as a consequence of hole (OI) hopping as a major contributing mechanism. This is the first observation of visible light-induced oxidation of a potential water oxidation complex by a metal charge-transfer pump in a nanoporous environment. These findings will allow for the assembly and photochemical characterization of well defined transition metal molecular units, with the ultimate goal of performing endothermic, multi-electron transformations that are coupled to visible light electron pumps in nanostructured scaffolds.
Date: June 3, 2008
Creator: Frei, Heinz; Weare, Walter W.; Pushkar, Yulia; Yachandra, Vittal K. & Frei, Heinz
Partner: UNT Libraries Government Documents Department